Hybrid electric vehicles having an internal combustion engine and an electrical propulsion motor each operable to provide drive torque to drive the vehicle, alone or in combination, are well-known. The propulsion motor is powered by a propulsion battery. The vehicle may be operated in an electric vehicle (EV) mode in which the engine is switched off and the electrical propulsion motor provides drive torque to drive the vehicle as required. The vehicle may also be operated in a parallel mode in which the engine is switched on and the electrical propulsion motor is operable either to provide drive torque in addition to the engine, in a parallel boost mode, or to generate electrical charge to recharge the propulsion battery, in a parallel recharge mode. A vehicle control system determines when to switch the internal combustion engine on or off, and when to open or close a clutch between the engine and a transmission. In some vehicles the electric propulsion motor is integrated into the transmission.
Also known are various vehicles which are exclusively electrically driven, in which an electrical propulsion motor alone provides the drive torque to drive the vehicle, the motor being powered by a propulsion battery which is rechargeable as or when required, for example at a recharging station.
Many examples of batteries used in known electric or hybrid electric vehicles generally require their internal temperature to be maintained within a carefully controlled temperature range in order to provide optimum performance and, especially, to be able to undergo charging or recharging at optimum efficiency. For this purpose such batteries generally require some kind of dedicated cooling system, which may be actuated as or when required in order to maintain the battery temperature at a desired level during operation of the vehicle. Such battery cooling systems are generally powered from the battery itself, or some other on-board charge storage device.
However, such battery cooling systems tend to be relatively power-hungry and use a relatively large amount of energy to run. It is increasingly important to seek to limit unnecessary energy wastage in motor vehicles. Furthermore reductions in electrical energy used by vehicle systems can enable a reduction in battery size, increased battery lifespan, and, in case of electric vehicles or hybrid electric vehicles, increased range of the vehicle.